Counter-Talk April 2010 — 1 Ron Hunsicker, P.E.

Brick Veneers in Earthquakes

Most research into the behavior of masonry in earthquakes involves reinforced, load bearing, concrete masonry. Generally, it is assumed that the reinforced concrete masonry absorbs all the energy from an earthquake and that masonry veneers contribute nothing. Masonry veneers are only expected to remain attached to the building—not fall to the street or sidewalk below. Recent research, summarized in the attached article from the December issue of The Construction Specifier, Seismic Performance of Modern Masonry.Construction Specifier.200912.pdf, indicates that clay brick masonry veneers contribute to resisting forces generated during earthquakes. Additionally, they do so while sustaining remarkably little damage. The motion of the 1994 Northridge earthquake was duplicated during the testing. This motion is often used because the ground accelerations during that earthquake were some of the highest ever recorded in an urban area in North America. (For comparison, the recent Haitian earthquake involved the release of about three times more energy than the Northridge earthquake; Mw 7.0 versus Mw 6.7.) Regardless, there was no damage to the veneers until the accelerations generated by the testing table were 20% greater than those found during the Northridge quake. Before you view Figures 11 and 12 and scream “How can a brick guy show that!” in the language of earthquakes, these two figures show “light” damage. The bricks did not fall off the building, the building did not collapse, and the structure can still function as intended. Although the cracks are large (to an East Coast or Midwest eye), they represent phenomenally good performance. If a building can still function after a large earthquake, it has done very well. Interestingly, when portions of the veneer fell from the residential building, it was not because the 22 gauge corrugated ties pulled out of the masonry. It was because the nails attaching the ties pulled out of the studs. Lesson: In higher seismic zones, use screws, not nails.